The present invention relates to apparatus for modulating a radio-frequency (RF) signal and, more particularly, to novel gated RF carrier modulation apparatus.
Apparatus for providing a gated modulated RF carrier signal is often required in the communications systems and allied arts. One known use of such apparatus is in the transmitter portion of an RF spectrometer utilized as part of a magnetic resonance spectometry and imaging system, such as described in co-pending application Ser. No. 714,405, filed on the same date as the present application and incorporated herein by reference in its entirety. Such gated modulator apparatus must provide a maximum isolation between input and output, i.e. have extremely high insertion loss, in the ungated ("gate open") state, yet provide minimum insertion loss in the gated (or "closed") state. Similarly, the amplitude of the RF carrier wave, when the modulator is in the gated condition, should follow the modulation signal waveform with a high degree of linearity.